Circuit boards provide both mechanical support and electrical interconnection of electronic components. Circuit boards generally use conductive traces etched from copper that has been laminated onto a non-conductive substrate. Circuit boards in radio frequency (RF) applications can use specially designed traces such as stripline or microstrip traces. These RF trace techniques may be used to control the transmission line characteristics, such as impedance, for traces that conduct RF signals.
Traditionally, a stripline trace is positioned within the layers of a printed circuit board (PCB) with a ground plane above and a ground plane below. In contrast, a microstrip trace is typically positioned on, or near, a surface layer of the PCB. As such, the conductors of the two trace types are generally on different PCB layers. Interconnection of such conductors on different PCB layers can be complicated and is generally achieved with one or more vias or plated holes placed through the board within an area where the conductors overlap. The geometries of the vias, contrasted to the geometries of the traces, often introduce undesirable discontinuities in impedance and other transmission line characteristics. Such imperfections in a signal path can increase noise and reduce the maximum operating frequency of the circuit.
Having a laminated planar structure, there is limited opportunity to provide vertical conductive elements, aside from vias, within the traditional PCB. As such, the construction of waveguide transmission paths is generally not supported. Furthermore, vertical shielding is limited. Due to this limited shielding, increased signal isolation generally requires increased distanced between traces, thereby increasing size, weight, and cost of the PCB.
Traditionally, electronic RF devices may be positioned upon a PCB. The height discontinuity between surrounding traces and the pads at the top of the device can introduce undesired signal effects when interconnecting the devices to the PCB traces. Furthermore, the routing of power and control signals to such devices can be quite complicated and is often accomplished at the expense of isolation, mass, and size.
Accordingly, there is a need in the art for a mixed-signal circuit board that can simultaneously support multiple transmission path technologies such as stripline, microstrip, suspended stripline, suspended microstrip, and waveguide while providing simplified transitions between paths of different transmission types. There is a further need in the art for the circuit board to support increased isolation between the transmission paths. There is yet another need in the art for the circuit board to support efficiently embedding electronic components within the transmission paths while simplifying the routing of control and power traces to the electronic components and without compromising signal path isolation.